1. Field of the Invention
The invention relates to a novel matrix wipe generator for television signals. More specifically, the invention relates to such a wipe generator giving the effect of a Z-axis wipe.
2. Statement of the Prior Art
Switching between two video signals to produce a special effect, such as switching from picture A to picture B halfway across the width of a picture, is a well known technique. Such switching can be accomplished by fast or soft transistions as well known in the art. When such a transition is moved along the width of the picture, the effect is known as a wipe, and the transition takes place over the entire screen in either a vertical or horizontal direction.
Matrix switching of two pictures is also known in the art. With this technique, the screen is divided into a plurality of blocks, and, if the screen originally contains picture A, then picture B is switched into the blocks one at a time until all of the blocks, i.e., all of the screen, are filled with picture B. Such a transition may be referred to as a matrix wipe, and the generator for producing this effect may be referred to as a matrix wipe generator.
With the matrix wipe generators of the prior art, the transition in each block is fast, i.e., there is an abrupt switch in the block from the A picture to the B picture. The waveform which produces the fast transition comprises a horizontal level (the A signal) followed by a rise in the level, at 90.degree. to the first level, and rising to a second level (the B level), and subsequently remaining horizontal at the second level.
The slow transition is initiated by a ramp signal proceeding from the first level to the second level. In the zone of the ramp, varying proportions of the A and B signal are added together, the net sum always being unity. Thus, the intensity of the A signal decreases as the intensity of the B signal increases. On the screen, the intensity of the A picture correspondingly decreases as the intensity of the B picture increases, until the B picture completely displaces the A picture.
Various switching and transition techniques are taught in, for example, U.S. Pat. Nos. 3,941,925--Busch et al--Mar. 2, 1976; 2,240,420--Schnitzer--Apr. 29, 1941; 2,784,246--Hurford--Mar. 5, 1957; and 2,193,869--Goldsmith--Mar. 19, 1940.
However, none of these patents, or any other teachings in the art known to applicant, teach a matrix wipe generator which gives the effect of a Z-axis wipe.